1. Field of the Invention
The present invention relates to a method of producing a plasma addressed display device having a liquid crystal cell and a plasma cell superimposed on each other with a dielectric sheet therebetween.
2. Description of the Related Art
In recent years, a plasma addressed display device formed by superimposing a liquid crystal cell and a plasma cell via a dielectric sheet has been proposed. FIG. 3 shows an example of this plasma addressed display device.
The plasma addressed display device of FIG. 3 has a flat panel structure wherein a liquid crystal cell 2 and a plasma cell 3 are superimposed via a dielectric sheet 4.
In the liquid crystal cell 2, a color filter substrate 21 is bonded to the dielectric sheet 4 at a predetermined clearance via a sealing material 22. On the surface of the inner side of the color filter substrate 21, strip-shaped data electrodes made of a transparent electrically conductive material, which are not illustrated, but extend in the row direction, are formed in parallel in a column direction (a perpendicular direction to the plane of the figure). A liquid crystal material is filled in the clearance, or space, between the color filter substrate 21 and the dielectric sheet 4, to form a liquid crystal layer 23. Although not shown in FIG. 3, spacers are arranged in the liquid crystal layer 23 so as to make the dimensions of the liquid crystal clearance uniform.
In the plasma cell 3, the plasma substrate glass 31 is spaced from the dielectric sheet 4 at a predetermined clearance. On the plasma substrate glass 31 on the dielectric sheet 4 side are formed strip-like display electrodes 32 made of nickel or the like which extend in the column direction and are formed in parallel to one another at a predetermined interval in the row direction. On these display electrodes 32, barrier ribs 33 made of an insulating ceramic or the like and having a narrower width than the display electrodes 32 are formed at an equal pitch to that of the display electrodes 32. The plasma substrate glass 31 faces the dielectric sheet 4 at a predetermined clearance via these display electrodes 32 and barrier ribs 33. These display electrodes 32 and barrier ribs 33 constitute the partition walls 5. The sealed spaces defined by these partition walls 5 constitute the plasma chambers 34. These plasma chambers 34 are formed so as to extend in the column direction at a predetermined interval in the row direction. An ionizable gas is sealed in the plasma chambers 34. The ionizable gas to be used is, for example, helium, neon, argon, a mixture of them, etc. In this way, the display electrodes 32 and the barrier ribs 33 serve as the partition walls 5 defining the plasma chambers and, at the same time, also serve as the clearance spacers of the plasma chambers. Note that the display electrodes 32 are connected to a driver circuit and are driven thereby so as to alternately serve as the anode display electrodes 32A and the cathode display electrodes 32K. A frit seal 35 of a low melting point glass or the like is arranged on the peripheral portions of the plasma substrate glass 31. The plasma substrate glass 31 and the dielectric sheet 4 are tightly bonded by this frit seal 35.
In the plasma addressed display device, the data electrodes and the plasma chambers 34 intersect with each other, the data electrodes serve as column driving units, the plasma chambers 34 serve as the row driving units, and pixels are defined at the intersections of the data electrodes and plasma chambers.
In such a plasma addressed display device, when a predetermined voltage is applied between an anode display electrode 32A and a cathode display electrode 32K, part of the gas in that plasma chamber is selectively ionized, a plasma discharge is generated, and an internal portion of the plasma chamber is maintained at substantially an anode potential. When a data voltage is applied to the data electrode in this state, the data voltage is written in the liquid crystal layer 23 via the dielectric sheet 4 at the pixels aligned in the column direction corresponding to the plasma chamber 34. When the plasma discharge is terminated, the plasma chamber 34 voltage floats, and the voltage written in the liquid crystal layer 23 at the corresponding pixel is held until the next write period (for example after one frame). At this time, the plasma chamber 34 acts as a sampling switch, and the liquid crystal layer 23 at the respective pixels acts as sampling capacitors.
As a result of the operation of the liquid crystal by the data voltage that is written from the data electrode 15 to the liquid crystal layer 23 at the respective pixels, the display is carried out pixel by pixel. Accordingly, by generating a plasma discharge and sequentially scanning the plasma chambers 34 in the row direction, which writes the data voltage in the liquid crystal layers 23 at a plurality of pixels aligned in the column direction, the display of a two-dimensional image can be carried out.
Briefly explaining the method of production of such a plasma addressed display device by referring to FIG. 4, first, as shown in FIG. 4(A), a display electrode pattern is printed on the plasma substrate glass 31 in the form of stripes by, for example, a screen printing method, then these stripes are dried or cured to form the display electrodes 32.
Next, barrier ribs 33 are superimposed on the already formed display electrodes 32 by repeatedly screen printing stripes so as to stack the ribs on the electrodes as shown in FIG. 4(B). In this case, repeated coating is carried out by repeating the screen printing to obtain a height of about 200 .mu.m for the barrier ribs 33. After the barrier ribs have reached a predetermined height by the printing steps, the assembly is sintered and the tops of the barrier ribs are ground to unify the heights of the barrier ribs at a predetermined height.
Then, as shown in FIG. 4(C), a frit seal 35 is formed on the peripheries of the plasma substrate glass 31 by a dispenser or the like, the dielectric sheet 4 made of glass is placed on the barrier ribs, the dielectric sheet is bonded to the plasma substrate glass via this frit seal 35, the plasma chambers 34 which are formed thereby are evacuated, and then a gas is injected into the chambers.
Next, a not illustrated orientation processing is carried out. As shown in FIG. 4(D), spacers 24 for making the thickness of the liquid crystal layer uniform are applied about the dielectric sheet 4. As shown in FIG. 4(E), the color filter 21 is bonded to the dielectric sheet 4 via the sealing material 22 to form a liquid crystal chamber, and the liquid crystal is then injected into the space between the dielectric and the color filter to obtain a plasma addressed display device shown in FIG. 3.
When the dielectric sheet 4 is placed on the barrier ribs 33 and bonded to the plasma substrate glass 31, as shown in FIG. 5, dust particles D of about 5 to 10 .mu.m or so in diameter is sometimes sandwiched between the joined surfaces of the barrier ribs 33 and the dielectric sheet 4. The dielectric sheet 4 is a thin glass plate having a thickness of about 50 .mu.m, and the liquid crystal layer to be formed on the dielectric sheet 4 has a thickness of about 7 .mu.m, and therefore if dust D having such a size is sandwiched between the barrier ribs 33 and the dielectric sheet 4, an unevenness of the gap of the liquid crystal layer 23 and as a result an unevenness of the liquid crystal display occurs. In addition to this, the dielectric sheet 4 which is constituted by the thin glass plate is pressed against the barrier ribs 33, and is caused to deform locally as it is pressed against the ribs in the parts over the dust particles D and sometimes the glass plate cracks. For this reason, a panel in which dust D has entered in this way is a sub-standard article and therefore causes an increase in manufacturing costs.